A map display device is known. It reads out a road map from a map database and displays the read road map on a displaying unit such as a liquid crystal display. For instance, a car navigation device is known as the map display device.
The car navigation system is equipped with a vehicle position detection device that detects a vehicle current position based on information obtained from a GPS receiver, a speed sensor, or the like. Position information obtained from the vehicle position detection device is displayed on the displaying unit with being overlapped on a road map. The car navigation device furthermore retrieves a route from the current position till a destination according to destination information obtained through user's manipulation. Routing assistance is thereby executed via voice or the like.
The road map used for retrieving the route preferably needs an actual road configuration to be reflected on it. When the road map used for retrieving the route is different from the actual road configuration, the car navigation mistakenly executes routing assistance. The user thereby advances to a wrong direction.
US Patent Application of US 2002/0077745 A1 discloses a system avoiding the above. Here, a map database is provided at an information center and seriatim updated by a person of the information center. The latest road map stored in the map database is thereby distributed to car navigations via wireless communications.
However, in the above case, the person at the information center cannot determine whether contents of the database are correct or not. Even when an actual road configuration is changed, the contents of the database cannot be immediately updated.